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Adafruit MAX31855 mobile interference
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Adafruit MAX31855 mobile interference

by ElGrigon on Sun May 12, 2019 6:43 pm

Hi,

I have working temp. reading and PWM heater control. Everything is working well except when I aproach my mobile phone nearby (cca 0-50cm) and esspecially when I run mobile data (video on youtube for examp.), I get false readings. Temperature jums around at random values, sometimes even in negative.
If I put my phone away from a board everything runs normall again.

I have Adafruit module with level shifter and 5VDC supply integrated. Signal leads are short - 0.5cm on breadboard. I have put some shield on thermocouple wires and ground it, doesn`t help.

Any idea what else could I do?

The last thing is to put the whole module in a metal case-shield. Maybe there is some electronic solution for this?

ElGrigon
 
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Joined: Sun May 12, 2019 6:34 pm

Re: Adafruit MAX31855 mobile interference

by adafruit_support_bill on Sun May 12, 2019 7:59 pm

Everything is working well except when I aproach my mobile phone nearby (cca 0-50cm) and esspecially when I run mobile data (video on youtube for examp.), I get false readings.

I guess the obvious question would be: Is there a need to play video on your phone in close proximity to the thermocouple?

Sensors like thermocouples work in the millivolt or microvolt range and can be easily influenced by electromagnetic interference in close proximity.

adafruit_support_bill
 
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Re: Adafruit MAX31855 mobile interference

by ElGrigon on Mon May 13, 2019 1:27 am

Yes. I'll use it in application where anyone can be near to a half a meter with a mobile phone web searching.

Interesting. I've never seen that mobile interference would influence on thermocouple.

I have some Chinesse PID controller that uses thermocouple and there is no false temp. reading if I try with a mobile phone.

Do you have any idea why Adafruit Max31855 has issues with that?

I want to make it work without these interferences instead switching to another module or IC.

ElGrigon
 
Posts: 3
Joined: Sun May 12, 2019 6:34 pm

Re: Adafruit MAX31855 mobile interference

by adafruit_support_bill on Mon May 13, 2019 5:51 am

I've never seen that mobile interference would influence on thermocouple.

The first law of electromagnetic interference is: "everything is an antenna." And a long loop of wire coupled to a high-gain amplifier makes a pretty good receiving station.

What are you using to shield the thermocouple probe? And how is it grounded? Some photos of your setup may help.

adafruit_support_bill
 
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Re: Adafruit MAX31855 mobile interference

by ElGrigon on Mon May 13, 2019 6:21 am

It's a shield from a cable, grounded at the end to GND of the power supply. Shield doesn't touch the probe.
Anyway there is no difference if shield is on or not.
I think that noise is picked up only by adafruit module. Maybe a design of PCB makes perfect scenario for mobile interference.

ElGrigon
 
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Joined: Sun May 12, 2019 6:34 pm

Re: Adafruit MAX31855 mobile interference

by adafruit_support_bill on Mon May 13, 2019 7:02 am

It is possible that the board might need shielding as well. Cell phones operate at fairly high frequencies, so even short traces can serve as an effective receiving antenna.

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